A lactate oxidase (LOD) gene from Aerococcus viridans was cloned and sequenced to generate thermostable LOD, One mutant LOD selected from a set of variants created by random mutagenesis had a half life of 6.2 min at 65 degrees C, approximately three times longer than that of the wild type LOD. This mutant exhibited an Asn to Asp point mutation at position 212 in the amino acid sequence.